Evolution Rehbit 4/22

Jean-Baptiste Lamarck (1744-1829)

Concluded more complex organisms descended from less complex organisms

Evolution

A change in a species over time

Two Wrong Ideas About Evolution

• Use and Disuse- if you don’t use a part, you lose it. The parts you use the most get stronger.

• Inheritance of Acquired Traits- the characteristics acquired by an organism during its lifespan are passed onto its offspring. Ex. if a person has an arm amputated then her children will not have arms

Experiment Disproving Lamarck’s Theory

• In late 1800s by August Weismann

• Cut off the tails of mice

• Mated the tailless mice

• Many generations

• The offspring of the tailless mice were always born with normal length tails

• Acquired traits are not inherited by offspring

Charles Darwin (1809-1882)

Proposed the theory of natural selection (mechanism of evolution) and was interested in how variation between members of a species provided adaptations unique to the environment

Overproduction in Natural Selection

Organisms produce more offspring than can possibly survive. (Darwin drew ideas from economist Thomas Malthus). Reasoned that the environment limits the populations of all organisms by causing deaths or limiting births.

Genetic Variation in Natural Selection

Many differences are found among individuals of a species due to meiosis and genetic inheritance

Competition in Natural Selection

Some variations provide “adaptations” (traits that help an organism to survive). They will compete with one another for survival.

Differential Reproduction in Natural Selection

Organisms with the best adaptations are most likely to survive and reproduce. Overtime, these adaptations will become more and more frequent in the population. Populations (group of individuals of the same species) may begin to differ as they become adapted to different environments.

How does evolution occur?

Overproduction —> Competition —> Survival of the fittest (organism with best adaptation for current environment) —> Natural Selection —> Reproduction

Adaptation (does not equal adapt)

Inherited traits that increases the chance of survival (not always “visible”)

Sources of Adaptation

Random Mutations

• Due to radiation, chemicals, pesticides, pollution, mistakes in DNA Replication, viruses, etc.

• Occur in both Asexually and Sexually Reproducing Populations

Events specific to Sexual Reproduction:

• Crossing-over of homologous chromosomes (meiosis)

• Independent assortment of chromosomes (meiosis)

• Random fertilization

Did Darwin know the source of these variations?

NO! He did not know about DNA or genes

Structural Adaptations

Physical appearance

• Large ears

• Thorns

Behavioral Adaptations

Control how an organism acts

• Hibernation

• Blooming only at night

Physiological Adaptations

Based on body chemistry and metabolism; usually don’t show

• Toxins in plants

• Desert animals have efficient kidneys

Inherited Behavioral Adaptations

• Migration

• Hibernation

• Being Nocturnal

• Defensive behaviors

• Mating or courtship behaviors

Learned Behavioral Adaptations

• How to find food

• Making a shelter

• How to communicate

• How to get along in a group

• Looking out for predators

Individual Behaviors

• Courtship

• Hibernation

• Mating

Group Behaviors

• Flocking

• Schooling

• Herding

• Team hunting

• Migrating

• Swarming

Cause for Natural Selection

Environment

Cause for Artificial Selection

Humans

Speed of change of Natural Selection

Slow

Speed of change for Artificial Selection

Fast

Reason for Natural Selection

The selected trait improves the organism’s chances of surviving and reproducing

Reason for Artificial Selection

The trait is desirable to human breeders

Effect of Natural Selection on fitness

Improves fitness (although only for the circumstances in which it is selected. If conditions change, (driving force for evolution) the selected trait may no longer be advantageous.)

Effect of Artificial Selection on fitness

Often causes decrease in fitness

ex. wolf —> dog